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Silent_Assassin

How to build an AEG MOSFET

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im not using the exact ones clot linked, but very similar specs, possibly lower in

the power disipation (cant remember, i have the spec sheet somewhere)

 

the one i can get to in the mp5 gets warm to touch in operation, though i cant tell

if its the switch of brake that gets warm fastest. i have just put shrink on the heat

sink of the lower fet to insulate the two from battery short (again untested).i only

noticed the cut out on the mp5 testing in the house, it was fine in the field, but i

relocated the fuse and the mosfet unit into the space infront of the trigger while it

was apart anyway to be safe.

 

i put bullets on the battery end of the fet unit to ease threading through aeg body

and install the fuse in the battery side. ak is in the stock, and mp5 switch unit and

fuse has now been relocated in the space in front of the trigger, will see how they

go.

 

i need to build another, and test current draw, battery short between heat sinc tabs,

removal of the small resistor.

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...

i put bullets on the battery end of the fet unit to ease threading through aeg body

and install the fuse in the battery side. ak is in the stock, and mp5 switch unit and

fuse has now been relocated in the space in front of the trigger, will see how they

go.

.....

 

Can you explain this better/in more detail? I am not quite understanding what you mean; maybe a picture? I'm not really sure what you mean by the space in front of the trigger; inside the gearbox?

 

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This one.

http://uk.rs-online.com/web/search/searchB...amp;x=0&y=0

And this one.

http://uk.rs-online.com/web/search/searchB...amp;x=0&y=0

 

I have used those to build AB mosfets, I also use 100R and 33K resistors.

 

Again, thanks for the info Blood-Clot. I'll order some of those fet's next week run some current draw tests and post my results.

 

Josh

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For the FET, there are 3 specs that you want to look for;

1. ID = Continuous Drain Current, in Amps. You want this to be a minimum of around 180Amps (at 25°C). There will be two figures quoted, one at 25°C and one at 100°C, which will be approx 30% lower.

2. PD = Power Dissipation, in Watts. You want a rating upwards of 200W. The higher it is, the more heat it can dissipate.

3. VDSS = Breakdown Voltage, in Volts. Wants to be around 35V or higher.

There are many other specs that will be quoted, but these are the three most important ones, get those right and the others will be good.

The other thing you're looking for is the 'package type', go for TO-220.

For a simple switching MOSFET build you want an N-Channel type, as opposed to a P-Channel, unless you want to build an AB MOSFET, in which case you'll need both types.

.........

One other question; are these stats the same that we should be looking for in P-channel FETs as well? And would it matter if you mix up different "package types" between the two FETs; i.e. a TO-220 N-channel and a TO-264 P-channel.

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post-40305-1247085713_thumb.jpg

 

in blue are the bullet connectors 2.5 or 3mm i cant recall but these help

with routing wiring out the front of the mp5 where the deans connector

is too large. on the ak i installed the fuse on the red wire of this extension

harness

 

the red area inside the mp5 body is a big open space with wire guides

running to the motor around the trigger. i installed the mosfet unit into

this space with plenty more room to install the fuseand trigger wires.

 

having the switch wires and unit in this space makes disassembly quite

simple with only the battery wires having to pass through the body, even

rear wire but i could not find the space for the connector.

 

hope that clears what you were after crack

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Ah ok, that makes sense now. Funny thing is I have one of my MP5 in pieces on my work table as I just overhauled it am putting in a 'FET, I didn't realize that was dead space; I will have to see if I can fit my AB 'FET there as well. Thanks! ;)

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same here, i had installed the fets up front on the fuse plate, but each time i stripped

it down i had to desolder the trigger wires to remove the gear box.

 

last time i stripped it down to replace hop parts i spotted this space below the gearbox,

from this space all i need is to remove motor and feed wires through the body to get

the gearbox out.

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Present for anyone ordering from RS before the end of this month, but only if you buying LOTS of stuff..... :

 

It’s easy to save money with RS. All you need to do is place an order over £100 at between now and the end of the month, add promotional code NBM69X to your order and your discount will be applied to your invoice.

 

If you happen to need that much kit, a tenner off 100 quid wont go a miss.

 

 

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DT, have you fitted any MOSFET's to any L85 series RIF Yet ?

I've fitted a simple switching MOSFET (non-AB) to an ARMY L85.

The extra speed caused it to over-run the passive braking (PB) 'pre-cocking' system, meaning it would fire a 2-round burst in semi, then pre-cock, then 2-round burst, etc.

L85 semi problem...

I sorted it in the end by re-working the PB contacts, but it would still occasionally do it with a fresh battery.

The owner now uses a 7.2V 2200mAh pack instead of the original 8.4V 2200mah pack and it's perfect.

 

Do the STAR and/or ARES versions have the pre-cocking feature?

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Present for anyone ordering from RS before the end of this month, but only if you buying LOTS of stuff..... :

 

It’s easy to save money with RS. All you need to do is place an order over £100 at between now and the end of the month, add promotional code NBM69X to your order and your discount will be applied to your invoice.

 

If you happen to need that much kit, a tenner off 100 quid wont go a miss.

Yeah, they send me this every time a place an order with them for enough stuff to make another ten fets.

 

Total inc p&p,,,,,,,,,,,,,,,,,,,,,£23. :(

 

 

Greg.

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